Magnetic body



106. COMPOS!Tl6? -S,-

H "A xi Eiaikw COATING OR-PLASVC 2 Au 11; 1931." H, LATHROP 1,818,070

MAGNETIC BODY Filed June 6, 1930 ATTORNEY Patented Aug. 11, 1931 umrao STATES PATENT ori ce nus'nsr. tunnel, or eansizwrcn, 'couuncrrcur. assrenoa 'ro BELL rmnrnom: monaroms, meoaronarnn, or nnw ronx, 1w. Y., a conroaarrou or mew YORK Application filed lane 8,

This invention relates to electrical insulation and particularly to the insulation of ma etic material in magnetic cores for loa 'ng coils and the like. a

An object of the invention is to improve the magnetic, electrical and mechanical characteristic of magnetic bodies of-the type em loying ma netic material in finely divi ed form, or example, magnetic dust cores for loading coils.

Magnetic cores made from finely divided magnetic material, so called magnetic dust cores, are bein extensively used for the loading coils which are inserted in telephone lines to improve their transmission characteristics. Such cores are usually constructed by subjecting the finely d1v1ded particles of the magnetic material and a non-magnetic, insulating and binding mag terial between the magnetic particles, to extremely high pressures in the neighborhood of 200,000 pounds per square inch. The high pressures are utilized to form the component materials into a substantially homogeneous mass in the desired core form, and to give sufiicient mechanical strength to the completed core. The non-magnetic material serves. as a-binder, and also as an insulation between the magnetic particles to reduce 3o eddy current losses in the completed core. In the case especially where the magnetic materiaLin a core made, in the above described manner is a magnetic alloy including nickel and iron, it has hitherto been 'found' desirable to subject the core to a subsequent heat treatment at a bi h temperature to remove the strains intro need in the magnetic material by the pressing operation, which tend to impair the magnetic roperties of the m etic allo in the core. lt is desirable, there ore, that t e insulatin material used in the core be one which w bind the magnetic particles firmly together, and which -Wl1l withstand without deterioration the high pressures and temperatures to which" it will be subjected during the constructionof the core. It is desirable also that the insulating material in the. core be one which will not deteriorate under the conditions to which loading coils are, sub

me'nnrrc non! 1930. Serial in, 459,504.

jected in service, so as to impair the magnetic, electrical or mechanical properties of j said coils.

' The U. S. patent to Andrews et al., No. 1,669,643, issued May 15, 1928, discloses a method of obtaining the above-mentioned desirable properties in a magnetic dust' core ess of manufacture disclosed in the Andrews et al. patent, the'magnetic cores in' which the sodium silicate-talc-chromic acid insulation is used are boiled in water prior to the final annealin -heat treatment in. order to make them 0 emically stable and to remove substantially all soluble substances such as chromates. Asa result ofconsiderable experimentation, applicant has discovered that magnetic dust cores having better magnetic and so electrical properties at least as good as those employing the sodium silicate-talc-chromic acid insulation may be roduced by using as the insulatin apd bindin material between the magnetlc dus't particles, merely talc andggdium silicate water glass% of a 1TH silicalgito so a re 10, in em a e propo fiions. en t e so um silicate. has a high silica to soda ratio, it was found unnecessary to use an additional chemical,l such as chromic acid, for neutralizin the a kali. The elimination of the chromic acid in the manual W515 1n a sunfilifi'cition of the process of manufacture of the magnetic dust cores for the steg of washing the cores" to remove .water solu le salts of the chromic acid is unnecessary.

The proportions of the sodium silicate and tale to be usedin a given case are deter- 1m mi! ad by the amount ofmagnetic material in the body,'the constituents of thematerial through a sieve of 120 meshes per in and them etic and electrical properties used as the magnetic core material. The desired in t e finalmagnetic body or core. magmatic dust particles are then insulated.

Briefly, the preferable rocess of making e material utilized for insulating the magnetic bodies in accor ance with the inmagnetic dust particles from each other m vention is as follows. The finely divided accordance with the invention comprisestalc ma U 'al and finely divided dry and sodium silicate only. The particular I a are first mixed to ther in the 'roperproportions of these materials. used depend 'roportions, and then ereis added ereto on the amount of magnetic material, the the pro r amount of a gether with the applipleted body. .Where the alloy dust constituents thereof an the magnetic and cation of heat thereto until the water is ticles have the preferable combinationo apevaporated and insulating coatings containproximately 81 per cent nickel and 19 per mg sodium silicate and talc are formed on cent iron and the are to be'u'sed for making the magnetic particles. A mass of the insumagnetic cores or coils for loading telelated particles which are of the uired phone circuits, the ma etic' dust particles .degree of fineness to make them suitable are-preferably insulate as.follows.

for use as magnetic core material, are then Finely divided is first thoroughly sub ected tohigh ressure to form them into mixed with the magnetic dust particles in a sohd, substan omogeneous mass of pro anging from 1.0 to 2:5grams,

rtions r the desired form, which is subsequently an- 'pre erably 1.5 grams, talc to each 100 grams g ealedat a high temperature to improve?! of the nickel-iron alloy dust. To this mixture is added a solution in about 20 C. C. of hot water of 0.5 to 2.0 grams preferably "aifi'sjsodium silicate to each grams ma etic pro rties of the ma etic ma- The practical applications of the i'nven- 1.

tion and the deta s thereof will be clear of t e magnetic alloy dust. .For the best 4 from the description when read in connecresults, the tale and sodium silicate used device, such as a loading coil, comprising cordance with the invention.

tion with the accompanying drawing, the should have a 51 h degrefi .gf pur'ty and the single figure of which illustrates ,a magnetic sodium silicate o d ave a in h silica t9 bggda ratio. The high ratio of silica E the toroidal win 1 and a magnetic core so a m e sodium silicate makes unneces- 2 therefor compose of a plurality of stacksary the use of an additional material like ed 'core rings made of compressed magchromic acid to neutralize the alkali in the netic dust and insulating material in 'acsodium silicate and also makes unnecessary the later ste of washing out undesired In carrying out the present invention, the water soluble sa ts, such as sodium chrommagnetic material is preferably prepared ate, the presence of which in the complete from a magnetic allo mclu make and cores would tend to make the magnetic and iron. A preferable cm of oy contains electrical roperties thereof deteriorate in approximately 81 per cent and a service. odium silicate is much less water proximately 19 per cent iron. esoluble than sodium chromate. The elim scription of this and other which may be used in the magne 0 es tages'from the manufacturing point of view of the invention reference is made to the since chromic acid is a hygroscopic highly U. S. patent of W. Elmen No. 1,586,884 oxidizing substance.

issued June 1i 1926. Obviously magnetic alloys other those described in that with the application of heat thereto until patent may also beused. The etic althe temperature of themass is about 120 oys used may be embrittled by e addi- C. in order to evaporate the water and to tionof an embrittlmg' it to a suitab e material or by subform on the magnetic dust particlesadherprelimina metalent insulating coatings urgical treatment such'as discl v for exsodium silicate. The insulated dust is then ample, in the ULS. patents to Zickrich No. sieved the 1 632,105 issued June 14, 1927, Beath et al. meshsieve N 0. 1,669,649 issued May 15, 1928, White coil core material. A mass of the inatent No. 1,73%052 and patent No. ted 739,068 both issued December 10, 1929. a mold After this it may be readily reduced to parsure approximately 200,000 pounds per ticles of the required degree of fineness, in square inch, into core rings suchas shown any well known manner, for example, by in the core 2 of the drawing. Following in a hammer'mill and then subthisste intheprocess,thecorerings,withenty rolling thecrushed particles in it out an ul exposing them'to the air, are.-

ba mill. The'resulting product is then tran'sfe to an ann furnace where sieved, and the portion thereof passing they are annealed at the optimum annealing electrical characteristics desired in the com-.

mggetic alloys ination of the chromic acid has other advan- Thewhole is then stirred. continuousl rtion passin thro h a 120 ging suitable ar use s a load-- comprising talc and magnetic particles is then placed in 7 an compressed under high pres- 106. COMPOSITIONS,

COATING P. Pl mm temperature of approximately 500 C., and are then cooled. A plurality of the rings thus formed are stac ed coaxially to form a core,-such as shown in the drawing, on which the usual loading coil core toroidal windings 1' are wound. The number, of rings used in a given core will depend upon the existing electrical characteristics of the telephone circuit with which the loading coils are to be associated.

It has been found that the magnetic dust cores com risin magnetic alloy particles and the ta c an sodium silicate insulation in the above mentioned proportions, made by the above mentioned process have for a given high permeability at least as good ysteresis and resistivity characteristics as arcores employing the chromic acidtalc-sodium' silicate insulation of the prior art making them particularly suitable for use as cores for loading telephone circuits. The insulation in these cores is a decided implrovement over the 1nsul' ation used hit erto in the prior art in that the required insulating and binding properties are obtained w1th a smaller number of chemical materials resultin in a more simplified and cheaper 'process. oreover, as brought out above the materials used for insulatin the magnetic dust particles in the cores-0 the invention do not form deleterious chemical combinations which tend to im air the magnetic electrical and mechanica characteristics of the cores under the conditions to which the loading coils are subjected in practice.

It is to be understood that the invention is not limited to magnetic bodies or cores made from magnetic materials having the particular constituents referred to nor to the particular proportions of the magnetic and insulating materials and to the par--.

' ticular heat treatments specified above,

A only between the allo consisting of sodium silicate havin which have been given by way of exam le only, and that other magnetic alloys 0t er proportions of the insulatin materia and other heat treatments may e employed in making such cores without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimedis:

1. A magnetic body consisting of finely divided nickel-iron alloy and an insulating and binding material comprising sodium silicate of high silica to soda ratio and talc particles.

2. A magnetic bo y comprising a magnetic alloy in finely divided form, including nickel and iron, and an insulating material between the particles of the alloyhang a silica to soda ratio, and talc only, t e whole compressed into a substantially homogeneous solid.

3. A magnetic body comprising finely cROs IaEFEIIEIIOI the magnetic alloy ture reac es a Examiner divided particles of a magnetic alloy including'nickel and iron in a proximate proportions of 81 per cent nic iron, and an insulating material between the particles comprising talc and sodium silicate, said insulating material constitutin approximately three per cent by weight 0 el and 19- per cent I the ma netic alloy, compressedinto a substantia form. I p '4. A magnetic body'comprising an alloy including approximately 81 per cent nickel finely divided form,

and 19 r cent iron, in

y homogeneous mass of the desired and an 1nsulating material between the parsodium silicate and talc ticles comprisin 0.5 to 2.0 per cent and 1.0

in proportions o to 2.5 per cent, respectively, the magnetic material.

5. A magnetic body comprising an alloy including approximately 81 per cent nickel and 19 per cent iron, infinely divided form, and an nsulating ticles' comprisin in groportions o approximatel an 1.5 per cent, respectively,

material. 6. The process of makin" a magnetic body comprising finely .divlded magnetic articles and an insulation material consistmg of talc and sodium silicate only, which process consists in continuously stirring together a mixture of the finely divided magsodium silicate and talc y weight of netic particles and finely dividedtalc in a solution of sodium silicate of high silica to while subiecting -the whole to the magnetic particles with talc soda ratio, heat, to coat and sodium silicate, subjecting a mass of the coated particles to hi h pressure to form itinto a substantially omogeneous 'solidof the desired. form, and subsequently heat treating said solid at a improve the ma netic material t erein. 7 The process of making a magnetic body which consistsin continuously stirring together a mixture of finely divided particles of iron-nickel alloy and finely divided talc in a water solution of sodium silicate while subjectin I the whole to heat until the mixtemperature ofapproximately 120 C., to insulate the alloy particles, subjecting high pressure to form it. into a substantially -homo eneous solid of the desired form, and

then eat treating saidsolid to improve its magnetic properties.

8. The process of making a magnetic core electrical and mehaving such magnetic,

to make it particuby weight of material between the par- 1.5 per cent high temperature to etic properties of the mag-.

a mass of the insulated particles to method consists in thoroughly with each 100 grams of the finely divided parti cles of said magnetic alloy approximately 1.5 grams of finely'divided talc, adding the mixture'to 'a water solution containi approximatel 1.5 grams of sodium si cate, continuou y stirring the whole together with the application of heat until it reaches a temperature of approximately 120 0., to

form insulating coatings comprising talc and, sodium sillcate on the magnetic articles, sub 'ecting a mass of the insulate particles'to h pressure to form it into a substantially okxogeneous solid of the desired form, and annealin said solid at a tempei'ature of approximately 500 C. to improve the m agnetic properties of the mag- V netie material therein.

In witness whereof, I hereunto subscribe my name this 5th day of June, 1930.

HUBBEL LATHROP. 

